According to the Daily Mail Online, Romney's in-house pollster Neil Newhouse finds the Republican is leading by a point in Ohio, two in Iowa, three in New Hampshire and is level in Wisconsin and Pennsylvania.

If those numbers are accurate, Romney would almost stroll into the White House. Even allowing for an element of spin, there could be a decisive late shift to Romney, driven by enthusiasm among Republicans and disillusion among Democrats.

Obama's aides know very well how polls can fail to reflect the views of late-deciding voters. In 2008 polls in New Hampshire showed the ingenue senator cruising to victory over Hillary Clinton in the Democratic primary, only for the former First Lady to win by two points as last minute voters moved her way.

Such an aberration across five, six or more states today seems less likely; Newhouse's numbers moreover contrast with all the final polls in the swing states, which a majority of which put the president narrowly ahead.

At this stage, or at any stage of the race really, there are polls and there are hunches.

"Any pollster who says 'this is how it's going to turn out' is crazy," says Andrew Smith, who conducts the University of New Hampshire's polling. His last poll, issued yesterday, has Obama up by three points in the state. But, he says, that slender lead could be overwhelmed by superior Romney turnout today.

With the race so close, the get-out-the-vote operations of each campaign will be critical. The Obama machine is the more sophisticated, but Romney's is the most advanced the Republican Party has ever seen and could even out the difference.

The Republicans have an advantage in that the groups less likely to turn out tend to be young people, those on lower incomes, who tend to vote Democrat.

"If we see a two per cent improvement in Republican turnout and a two per cent drop in Democrat turnout it would be decisive. That's why everybody is thinking the same way, that it will come down to turn out."

Mr Smith thinks the most likely outcome is a narrow Romney victory, followed by a narrow Obama victory and a comfortable Romney win.

"The key decision for voters is not who they are going to vote for, but whether or not they will vote at all," he says.